In recent years, a thermoplastic elastomer which has rubber elasticity, requires no vulcanization step, and can be molded and recycled similar to a thermoplastic resin is frequently used in the field of automobile parts, household appliance parts, wire coverings, medical parts, miscellaneous goods, footwear, and the like.
Especially, a hydrogenated product of a block copolymer containing a diene-based polymer block as a soft segment in a polymer chain (hereinafter, referred to as a hydrogenated block copolymer) has elasticity and feeling close to that of conventional vulcanized rubber. Therefore, it is expected to be applied as a raw material for molded articles in which vulcanized rubber has so far been used.
However, although the above hydrogenated block copolymer has rubber elasticity at ordinary temperature and can be easily molded by plasticizing and melting by heating, its heat resistance, oil resistance, and rubber elasticity under high temperatures cannot be said to be satisfactory. Therefore, there is a problem that the hydrogenated block copolymer cannot be used for applications where such properties are highly required.
In view of the problem, several proposals have been made on an elastomeric composition using the hydrogenated block copolymer.
For example, there has been proposed a technique of improving compression set under high temperatures by crosslinking an elastomeric composition in which the hydrogenated block copolymer is blended with a hydrocarbon oil, an olefin-based polymer and the like, using a crosslinking agent such as an organic peroxide and a crosslinking auxiliary (for example, refer to Patent Documents 1 to 3).
There has also been proposed a technique of improving oil resistance and rubber elasticity at high temperatures by crosslinking an elastomeric composition in which the hydrogenated block copolymer, a functionalized hydrogenated block copolymer, a polyamide resin, a hydrocarbon oil and the like are blended with each other, using a crosslinking agent such as an organic peroxide and a crosslinking auxiliary (for example, refer to Patent Document 4).
However, although crosslinked elastomeric compositions containing a conventional hydrogenated block copolymer as described above have recyclability which is a feature of a thermoplastic elastomer, a soft segment composed of a conjugated diene monomer block of the hydrogenated block copolymer is excessively crosslinked. As a result, there is a problem that the elongation of the resulting composition is significantly reduced, which poses a problem in the development of high rubber elasticity.
On the other hand, Patent Document 5 described below proposes a hydrogenated block copolymer having a block containing an unsaturated group at a molecular chain end, and it describes, as an Example, a hydrogenated block copolymer composition having a styrene/isoprene copolymer block at a molecular end.
However, according to this technique, the size of the block containing styrene monomer units is designed very small, which poses a problem of reducing the cohesion of styrene blocks and increasing the compression set of the hydrogenated block copolymer.
Patent Document 1
    Japanese Patent Application Laid-Open Publication No. 59-131613Patent Document 2    Japanese Patent Application Laid-Open Publication No. 08-225713Patent Document 3    Japanese Unexamined Patent Application Publication No. 2000-109640Patent Document 4    Japanese Unexamined Patent Application Publication No. 2004-197035Patent Document 5    Japanese Examined Patent Application Publication No. 07-116271